Measurement of ultrafine Particles (2 to 800 nm) in the Rhein-Main area with a special Emphasis on Airport Emissions

In recent years, the importance of ultrafine particle (UFP) measurements has increased significantly, particularly due to their adverse health effects. For this reason, it is important to further investigate and characterise strong UFP sources, especially in densely populated urban and suburban areas, to shed more light on their impact on local air quality. Former studies have already shown that highly frequented airports are a major source of UFPs (Hudda et al. 2014, Keuken et al. 2015); these studies further showed that even over long distances of up to 10 km downwind of the airport, UFP concentrations are significantly elevated. In this study, we deployed a variety of instruments to characterise the UFPs from Frankfurt Airport (FRA) in the densely populated Rhein-Main area. Size and concentration levels over a size range from 2-800 nm were measured at three different locations which are located 4, 8, and 15 km away from the airport, respectively. Overall, the measurements were conducted over a duration of 6 months. As a result, we found that aerosol emissions from the airport dominate the aerosol population of the neighbouring districts (up to a distance of at least 15 km) to a great extent. This can be seen when comparing particle number concentrations downwind of the airport versus urban background levels. The average diurnal particle number concentration at the closest measurement station with a distance of 4 km from the airport is elevated by almost a factor of 6 during the airport operating hours (05:00 – 23:00) compared to the urban background when the wind is arriving from the airport. Additionally, we found that the particle number concentration of diameters above 3 nm is up to a factor of 5 to 6 higher than the fraction above 10 nm, indicating that a large fraction of aircraft aerosol emissions is below 10 nm in size and therefore remains mostly undetected by standardised UFP measurements. This suggests that the particle burden can be significantly underestimated when only focussing on particles larger than 10 nm. In the presentation a detailed analysis of the measured results at the three different stations will be presented. The analysis focuses on the dependence of the diurnal pattern of the aerosol size distribution as a function of the origin of the air masses (wind direction). This way, airport emissions can be distinguished from other traffic emissions and the urban background. Furthermore, we present direct evidence that landing airplanes can contribute significantly to the smallest measurable particles < 10 nm. Overall, we conclude that for a full assessment of the negative health effects of UFP emissions it is important to (1) increase the number of monitoring stations, especially in areas with strong sources such as airports and (2) lower the size of the smallest particles that are detected from 10 to 3 nm, in order to determine the UFP concentrations and health risks more realistically.